Presentation on theme: "1 ODOT BRIDGE LOAD RATING A basic how and why overview."— Presentation transcript:
1 ODOT BRIDGE LOAD RATING A basic how and why overview
2 What is a Bridge? Federal Highway Administration (FHWA) Definition: A Bridge is ANY structure that… 1.) is erected over a depression or obstruction (water, highway, railway, etc.) AND 2.) has a track or passageway for carrying traffic or moving loads AND 3.) has an opening greater than 20-0 (measured along centerline of roadway between undercopings of abutments or spring lines of arches, or extreme ends of openings for multiple boxes; it may also include multiple pipes, where the clear distance between openings is less than half of the smaller contiguous opening)
3 What is a Bridge? (cont.) Ohio Department of Transportation (ODOT) Definition (based on the Ohio Revised Code): A Bridge is ANY structure that… 1.) is on, above, or below a highway AND 2.) Is greater than or equal to 10-0 (measured the same way as in the FHWA definition)
4 The Load aspect of Bridge Load Rating
5 There are Two Primary Types of Loads used in Load Ratings? Permanent or Dead Loads – Structure self weight – Superimposed dead loads (barriers, overlays, utilities, etc.) Transient or Live Loads – Vehicular loads – Impact loads
6 Three Types of Live Loads in Ohio Design or inventory loads – HS20-44, HS25, HL-93 Ohio Legal Loads – 2F1, 3F1, 4F1, 5C1 Permit Loads & S uperloads Note: The Feds only require highway loads to be used for load rating. Consequently, even though pedestrian and railroad structures fall under the definition of Bridge, and they are inspected and inventoried, they are not load rated
13 What Is Bridge Load Rating? The safe live load carrying capacity of a highway structure is called its load rating. It is usually expressed as a (rating) factor (RF) of a defined vehicle OR as a gross tonnage for a defined vehicle axle configuration
14 Basic Equation for Calculating the Rating Factor (RF) A load rating can be expressed in terms of a rating factor for a particular vehicle. RF = C – A 1 * D A 2 * L*(1 + I) A 1 = Factor for dead loads A 2 = Factor for live load C = Capacity of the bridge D = Dead load effect I = Impact factor L = Live load effect How to calculate the rating factor (RF)
15 Three Different Load Rating Methods Allowable Stress (ASD) Also known as Working Stress (WSD) Used for ODOT steel trusses and timber structures Load Factor (LFD) Load Factor (LFD) ODOT PreferredODOT Preferred FHWA PreferredFHWA Preferred Load & Resistance Factor Rating (LRFR) NCHRP Project 12-46
16 Two Types of Ohio Load Ratings Inventory Rating (Design Level) 1.) HS20-44 Operating Rating (Service Level) 2.) HS ) 2F1 4.) 3F1 5.) 4F1 6.) 5C1 Every bridge in Ohio has six different load rating factors calculated.
17 Factors for LFD Load Rating Ref: AASHTO Manual for Condition Evaluation of Bridges 2000
18 What components of a bridge is ODOT interested in Load Rating All primary superstructure components of a bridge shall be load rated. Unless specified in a scope, this excludes the following: Decks (unless bridge is a deck slab type) Bearings Substructures Field splices Railing / Parapets
19 When Should a Load Rating be Revised? The load rating of a bridge should be revised when: 1. there is a change in the dead load on the structure 2. there is a physical change in any structural member of the bridge. 3. there is a change in the proposed live loading 4. A different method of analysis is required
20 Why do we rate structures?
21 The Dec. 15, 1967, collapse of the Silver Bridge at Point Pleasant, Ohio killed 46 people. The failure of the 39 year old eye bar suspension bridge across the Ohio River prompted US Congress to pass National Bridge Inspection Standards (NBIS) in The Silver Bridge Collapse
22 Required by Federal government (NBIS) To monitor safety of structures over time To help determine when rehabilitation or replacement is needed Why do we rate structures? (2)
23 To determine if a bridge needs to be posted for a load restriction as required by the Ohio Revised Code To have a consistent summary of load carrying capacities of all state bridges To assist Office of Permits in their processing of Permit and Superloads
24 What is a Permit or Superload Vehicle?
25 A Permit* load equals… any vehicle or combination of loads having a gross weight in excess of 40 tons (or 80 kips). * = Permits are also required for over-SIZED vehicles. But, for the purposes of load rating, we are referring to permits that are required due to over-weight only.
26 A Superload equals… any vehicle or combination of loads having a gross weight in excess of 60 tons (or 120 kips).
27 Vehicle Categories based on weight Gross weight of heaviest Ohio Legal Load (5C1) 1.50 * 40
28 How many vehicle permits are issued each year?
29 Of those permits issued, how many are for Superload vehicles?
30 How many Superload routes does the OSE check each year?
31 Computer programs to assist in load rating ODOT bridges AASHTO BARS-PC (SHALL be used where possible) (http://www.dot.state.oh.us/srg/download.htm) BRASS (SHALL be used for buried structures) (http://www.dot.state.wy.us/generic/brass/index.html)
32 Additional Computer programs to assist in load rating ODOT bridges DESCUS I (www.opti-mate.com) STAAD III/Pro (www.reiusa.com) GT STRUDL (Finite Element based) (www.gtstrudl.gatech.edu) SAP 90 / SAP 2000 (Finite Element based) (www.csiberkeley.com)
33 1) Can run Batch routines (useful for fast analysis of superload routes) 2) Fast, free, and doesnt require a lot of resources 3) Tested and used over the last 20+ years 4) Provides output in rating format 5) Supports both Mainframe and PC computers 6) Custom vehicles can be easily defined 7) Useful for reviewing new designs Why is BARS desirable to ODOT?
34 The program and instruction manuals can be downloaded for free at… An introductory tutorial can be downloaded at… BARS on the Internet
37 BURIED STRUCTURES – ALL bridges (> 10) with fill > 2-0 shall be considered buried and shall be load rated EXCLUDING… Circular Steel pipes Circular Plastic pipes Circular Concrete pipes Buried Metal Boxes Buried Metal Frames Junction Chambers Manholes Inlets
39 NON-BURIED STRUCTURES – ALL bridges (> 10) with fill < 2-0 (or no fill at all) shall be considered non-buried and shall be load rated – BARS-PC SHALL BE USED when possible – BRASS-Culvert SHALL BE USED for concrete boxes and three-sided culverts – OSE MUST be contacted if any other software is going to be used
40 MISCELLANEOUS INFORMATION – Only load rate spans or portions of buried structure that will experience live load – Load ratings of new or rehabilitation bridge projects shall be based on final design plans and shall show results that meet or exceed the design loading – No FWS shall be included in load ratings
41 WHEN DO YOU SUBMIT YOUR ANALYSIS? MAJOR OR MINOR PLAN DEVELOPMENT (OR DESIGN BUILD) PROCESS –Include load rating report with STAGE 2 submittal ** MINIMAL PLAN DEVELOPMENT (OR DESIGN BUILD) PROCESS –Include load rating report with STAGE 3 submittal ** **Revise and resubmit load rating to District Project Manager if design plans change after Stage 2 (or Stage 3) and prior to contract sale
43 WHAT DO YOU PUT IN THE REPORT? A full project description Printouts of analysis software input/output Explanation of how material properties were determined (for existing structures) All hand calculations A table summarizing the following rating factors for each live load truck… Inventory & Operating ratings for each main bridge member analyzed (Beam 1, Beam 2, Interior, Exterior, etc.) Overall ratings of each structure unit (mainline, ramps, etc.) Overall ratings of entire bridge
45 WHAT DO YOU SUBMIT TO ODOT? 2 - Printed copies of load rating report (signed and sealed by an Ohio PE) 1 - Electronic copy of load rating report 1 – Electronic copy of input data files BARS - LISTA.LIS, RATE2.LIS, SUMMARY.LIS, and FLEX.LIS files BRASS - Files with the following extensions: DAT, CUS, and XML
46 AASHTO Load Rating References AASHTO (2002), Standard Specifications for Highway Bridges, 17th ed., AASHTO (2000), Manual for Condition Evaluation of Bridges, 2 nd Edition. (Section 6) AASHTO (1995), Bridge Analysis and Rating System, BARS-PC, Release 5.5, Mod 3.3, Users Manuals I and II,
47 AASHTO Load Rating References (cont.) AASHTO (1989), Guide Specifications for Strength Evaluation of Existing Steel and Concrete Bridges AASHTO (1978), Guide Specifications for Fracture Critical Non-Redundant Steel Bridge Members
RATING FACTORS BASED ON SHEAR CAPACITY (non-composite)
Composite Steel & Conc. Rating Factors (1)
OPERATING (composite, based on Moment Capacity) * whichever is smaller
RATING FACTORS BASED ON SHEAR CAPACITY INVENTORY
RATING FACTORS BASED ON SHEAR CAPACITY OPERATING where Vp = shear yielding strength of the web
Reinforced Concrete Rating Factors (1)
Prestressed Concrete Rating Factors (1)
65 Appendix 2 – Load Rating Example
66 Single-span slab bridge Bridge #: SEN Over: Branch of Wolf Creek SFN: Clear Span: 16-0 Slab thickness: 11.5 Slab Width: 40.5 ft Overlay: 3 asphalt on ¾ soil Long. Bottom Steel: 4 ½ Transverse Bottom Steel: 5s Analysis Software: BARS-PC Input filename: R DAT
68 AASHTO Standard Specification for Highway Bridges CASE B – Main Reinforcement Parallel to Traffic S = Effective Span length in feet (AASHTO ) For wheel loads, the distribution width E = *S 7 S = 16+1 = 17 feetE = *17 = 5.02 feet BARS Dist. = 1/5.02= Live load distribution factor
69 AASHTO Standard Specification for Highway Bridges Impact Formula The amount of impact allowance, I, as a fraction of the live load I = 50 / (L + 125) 0.3 L = Effective Span length in feet I = 50 / ( ) = 0.352Use I = 0.3 Impact load (Impact factor)
70 ((3 / 12)* 1 ft* 145 pcf) + ((3/4 /12) * 1 ft * 120 pcf) + 12 plf guardrail = 55.8 lb/ft Superimposed Dead Load Rebar distance to top of slab (11.5–1 clear due to delamination- 5/8–(7/8) / 2 ) =
71 Interactive Bridge Data Entry AA NEW X DMH - B&N *LF* POST 03 1SPEC SPEC DMH - B&N BSEN LF SEN OVER BRANCH OF WOLF CREEK, SFN: SINGLE SPAN CONCRETE SLAB BUILT IN 1926, 16 FOOT CLEAR SPAN " ASPHALT W.S. (DATE: N/A) ON 0.75" OF SOIL, 40.5' SLAB WIDTH S RC S01 01 W S S